1. Field of the Invention
This invention is concerned with epoxy based resins water-solubilizable with ammonia or an amine and with water based coating compositions containing them.
2. Description of the Prior Art
It has been proposed to form water dilutable emulsions or dispersions containing epoxy resins for use as water based coatings. Such coatings have disadvantages, and it is highly desirable to provide water-soluble epoxy based coatings. Prior epoxy based coatings have poor shelf life due to the presence of oxirane groups and/or unreacted anhydride.
In copending application Ser. No. 736,984, filed Oct. 29, 1976 now U.S. Pat. No. 4,105,614, there is disclosed a resin in which the epoxy groups of a diglycidyl ether are capped with a bisphenol and the resultant material is reacted with an anhydride to provide water-solubilizable carboxyl groups. The resins of this invention utilizing a monocarboxylic acid, such as stearic acid, have advantages over the resins of Ser. No. 736,984.
1. Coatings made therefrom do not absorb n-heptyl p-hydroxybenzoate, a preservative used to stabilize unpasturized beer.
2. Coatings made therefrom have less effect on the flavor of beer on short term storage.
3. The coating formulations have higher solids content at application viscosity, which permits use of a single coating to attain coating weights necessary in standard applications. Application viscosity is generally 15-100 sec., preferably 25-70 sec., #2 Zahn cup.
4. The final coating formulation has better shelf life, as measured by viscosity change.
In U.S. Pat. No. 3,355,401 to Tanner, there is disclosed a resin prepared by condensing a polyglycidyl ether of a bisphenol with (a) a monobasic fatty acid, and (b) a fatty acid having at least two carboxyl groups, at least one of which is attached to a polymethylene group of at least 4 carbon atoms. The reaction involved in this patent is a condensation reaction involving the elimination of water of condensation. On the other hand, the resin of this invention is prepared by adduction of monocarboxylic acid to the oxirane ring, which does not involve formation of water of condensation. The effect of this adduction, using 1:1 to 1:1.2 equivalent ratio of diglycidyl ether to monocarboxlic acid, is to cap all the epoxy groups.
As is well known to those skilled in the art, reaction of a carboxylic acid with an epoxy resin can inolve three types of reaction: (1) addition esterification by adduction of carboxyl to oxirane with no water of condensation, (2) condensation esterification by reaction of carboxyl with hydroxyl groups on the epoxy resin, with elimination of water of condensation, and (3) esterification by reaction of oxirane with hydroxyl groups on the epoxy resin, leading to possible undesirable gel formation. In the absence of catalyst and at elevated temperature (200.degree. C.), the reactions compete in a ratio of addition/condensation/etherfcation of about 2/1/1. In the presence of a tertiary amine catalyst, the only reaction is addition until all carboxyls are used up. Then, if some oxirane remains, etherification proceeds. See Lee and Neville "Handbook of Epoxy Resins", pages 5-18 through pages 5-20, McGraw Hill (1967).
Tanner operates at 185.degree.-215.degree. C. with no catalyst. Applicants use a tertiary amine catalyst and operate at about 150.degree. C., thereby producing a resin different from Tanner's.
Insofar as is now known, a resin system of this type and coatings containing them have not been proposed.